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United States Patent |
5,028,513
|
Murakami
,   et al.
|
July 2, 1991
|
Process for producing printed circuit board
Abstract
The present invention provide a process for producing printed circuit
boards which comprises the steps of
(a) roughening a surface of a copper layer formed on an insulating board.
(b) coating the roughened surface of copper layer with a photo-resist layer
containing a sublimable copper-corrosion inhibitor, exposing the resist
layer selectively to actinic rays according to a circuit pattern to form,
and developing the resulting resist layer, thereby forming plating-resist
coats on circuit-negative pattern portions of the copper layer,
(c) heat-treating the plating-resist coats,
(d) plating chemically the circuit-corresponding portion with copper,
(e) removing the plating-resist coats, and
(f) removing the copper layer except the circuit-corresponding portion
thereof.
Inventors:
|
Murakami; Kanji (Mito, JP);
Kawamoto; Mineo (Hitachi, JP);
Tadokoro; Akio (Ibaraki, JP);
Akahoshi; Haruo (Hitachi, JP);
Narahara; Toshikazu (Ibaraki, JP);
Toba; Ritsuji (Hadano, JP);
Ishimaru; Toshiaki (Hitachi, JP);
Hayashi; Nobuyuki (Hitachi, JP);
Wajima; Motoyo (Yokohama, JP)
|
Assignee:
|
Hitachi, Ltd. (Tokyo, JP);
Hitachi Chemical Co., Ltd. (Tokyo, JP)
|
Appl. No.:
|
336771 |
Filed:
|
April 13, 1989 |
Foreign Application Priority Data
Current U.S. Class: |
430/315; 430/314; 430/318; 430/329; 430/330 |
Intern'l Class: |
G03C 005/00 |
Field of Search: |
430/315,330,314,318,329
|
References Cited
U.S. Patent Documents
3622334 | Nov., 1971 | Hurley et al. | 430/281.
|
3854973 | Dec., 1974 | Mersereau et al. | 428/528.
|
3873316 | Mar., 1975 | Velten et al. | 430/159.
|
Foreign Patent Documents |
50-9177 | Apr., 1975 | JP.
| |
61-176192 | Aug., 1986 | JP.
| |
Primary Examiner: Bowers, Jr.; Charles L.
Assistant Examiner: Pezzner; Ashley I.
Attorney, Agent or Firm: Antonelli, Terry, Stout & Kraus
Claims
What is claimed is:
1. A process for producing printed circuit boards which comprises the steps
of
(a) roughening a surface of a copper layer formed on an insulating board,
(b) coating the roughed surface of copper layer with a photo-resist layer
containing a sublimable copper-corrosion inhibitor, exposing the resist
layer selectively to actinic rays according to a circuit pattern to form,
and developing the resulting resist, thereby forming plating-resist coats
on circuit-negative pattern portions of the copper layer,
(c) heat-treating the plating-resist coats,
(d) plating chemically the circuit-corresponding portion with copper,
(e) removing the plating-resist coats, and
(f) removing the copper layer except the circuit-corresponding portion
thereof.
2. The process of claim 1, wherein the sublimable copper corrosion
inhibitor is selected from the group consisting of benzotriazole,
methylbenzotriazole, benzoguanamine, guanidine, 1-cyanoguanidine,
thiazole, thiourea, 2-quinolylamine, 1,1'-azonaphthalene,
dicyclohexylamine nitrite, diisopropylammonium benzoate, cyclohexylamine
benzoate, and dicyclohexylammonium cyclohexanecarboxylate.
3. The process of claim 1, wherein the heat treatment in the step (c) is
conducted at a temperature where the plating-resist coats do not deform.
4. The process of claim 1, wherein the heat treatment in the step (c) is
conducted at a temperature of 100.degree. to 180.degree. C. for a period
of 1 to 2 hours.
5. The process of claim 1, wherein the removal of the copper layer except
its circuit pattern portion, in the step (f) is carried out after the
copper circuit pattern has been covered with a etching-resist layer.
6. A process for producing printed circuit boards which comprises the steps
of
(a) roughening of a copper layer formed on an insulating board, and
covering the roughened surface with a thin film of metal having a more
negative reduction potential of oxide than that of copper,
(b) coating the thin metal film surface with a photo-resist layer
containing a sublimable copper-corrosion inhibitor, exposing the resist
layer selectively to actinic rays according to a circuit pattern to form,
and developing the resulting resist, thereby forming plating-resist coats
on circuit-negative pattern portions of the thin metal film,
(c) heat-treating the plating-resist coats,
(d) plating chemically the circuit-corresponding portion with copper,
(e) removing the plating-resist coats, and
(f) removing the thin metal film and the copper layer except their
circuit-corresponding portion.
7. The process of claim 6, wherein the sublimable copper-corrosion
inhibitor is selected from the group consisting of benzotriazole,
methylbenzotriazole, benzoguanamine, guanidine, 1-cyanoguanidine,
thiazole, thiourea, 2-quinolylamine, 1,1'-azonaphthalene,
dicyclohexylamine nitrite, diisopropylammonium benzoate, cyclohexylamine
benzoate, and dicyclohexylammonium cyclohexanecarboxylate.
8. The process of claim 6, wherein the heat treatment in the step (c) is
conducted at a temperature where the plating resist coats do not deform.
9. The process of claim 6, wherein the heat treatment in the step (c) is
conducted at a temperature of 100.degree. to 180.degree. C. for a period
of 1 to 2 hours.
10. The process of claim 6, wherein the removal of the copper layer and the
thin metal film except their circuit pattern portions, in the step (f), is
carried out after the copper circuit pattern has been covered with a
etching-resist layer.
11. A process for producing printed circuit boards which comprises the
steps of
(a) roughening a surface of a copper layer formed on an insulating board,
and oxidizing and then reducing the roughened surface of copper layer,
(b) coating the treated surface of copper layer with a photo-resist layer
containing a sublimable copper-corrosion inhibitor, exposing the resist
layer selectively to actinic rays according to the circuit pattern to
form, and developing the resulting resist, thereby forming plating-resist
coats on circuit-negative pattern portion of the copper layer,
(c) heat-treating the plating-resist coats,
(d) plating chemically the circuit-corresponding portion with copper,
(e) removing the plating-resist coats, and
(f) removing the copper layer except the circuit-corresponding portion
thereof.
12. The process of claim 11, wherein the sublimable copper-corrosion
inhibitor is selected from the group consisting of benzotriazole,
methylbenzotriazole, benzoguanamine, guanidine, 1-cyanoguanidine,
thiazole, thiourea, 2-quinolylamine, 1,1'-azonaphthalene,
dicyclohexylamine nitrite, diisopropylammonium benzoate, cyclohexylamine
benzoate, and dicyclohexylammonium cyclohexanecarboxylate.
13. The process of claim 11, wherein the heat treatment in the step (c) is
conducted at a temperature where the plating-resist coats do not deform.
14. The process of claim 11, wherein the heat treatment in the step (c) is
conducted at a temperature of 100.degree. to 180.degree. C. for a period
of 1 to 2 hours.
15. The process of claim 11, wherein the removal of the copper layer except
its circuit pattern portion, in the step (f) is carried out after the
copper circuit pattern has been covered with a etching-resist layer.
16. A process for producing printed circuit boards which comprises the
steps of
(a) Roughening a surface of a copper layer formed on an insulating board,
oxidizing and then reducing the roughened surface of copper layer, and
covering the treated surface with a thin film of metal having a normal
negative reduction potential of oxide than that of copper,
(b) coating the thin metal film surface with a photo-resist layer
containing a sublimable copper-corrosion inhibitor, exposing the resist
layer selectively to actinic rays according to a circuit pattern to form,
and developing the resulting resist, thereby forming plating-resist coats
on circuit-negative pattern portions of the thin metal film,
(c) heat-treating the plating-resist coats, (d) plating chemically the
circuit-corresponding portion with copper,
(e) removing the plating-resist coats, and
(f) removing the thin metal film and the copper layer except their
circuit-corresponding portions.
17. The process of claim 16, wherein the sublimable copper-corrosion
inhibitor is selected from the group consisting of benzoytriazole,
tolyltriazole, benzoguanamine, guanidine, 1-cyanoguanidine, thiazole,
thiourea, 2-quinolylamine, 1,1'-azonaphthalene, dicyclohexylamine nitrite,
diisopropylammonium benzoate, cyclohexylamine benzoate, and
dicyclohexylammonium cyclohexanecarboxylate.
18. the process of claim 16, wherein the heat treatment in the step (c) is
conducted at a temperature where the plating-resist coats do not deform.
19. The process of claim 16, wherein the heat treatment in the step (c) is
conducted at a temperature of 100.degree. to 180.degree. C. for a period
of 1 to 2 hours.
20. the process of claim 16, wherein the removal of the copper layer and
the thin metal film except their circuit pattern portions, in the step
(f), is carried out after copper circuit pattern has been covered with a
layer of etching-resist for copper.
21. The process of claim 1, wherein the heat-treating of the plating-resist
coats is effected at a temperature and for a period of time sufficient to
cause partial removal of the sublimable copper-corrosion inhibitor from
the plating-resist coats whereby elution of the copper-corrosion inhibitor
into a chemical plating solution for effecting the chemical plating with
copper in step (d).
Description
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
The present invention relates to a process for producing printed circuit
boards and more particularly to a process for producing printed circuit
boards, for which fine, high-density patterns of circuits are required
today to have.
2. DESCRIPTION OF THE PRIOR ART
Conventionally, printed circuit boards with high-density patterns of
circuits, such as double-sided printed circuit boards and multilayer
printed circuit boards, have been fabricated mainly in the manner that
copper-clad laminates are used as starting materials, through holes
electroplated with copper are formed in the laminates, and the copper
claddings except their circuit-corresponding portions are removed by
etching. This conventional process is unfit for the fabrication of fine,
high-density circuits because the application of copper electroplating
results in large variation in plating thickness and the dimensional
accuracy of circuits depends upon both the exactness of etching-resist
formation and the exactness of copper etching. Therefore, various methods
have been proposed for the fabrication of finer, higher-density circuits.
One of these methods is the chemical (electroless) copper plating pattern
(selective electroless copper plating of conductive patterns) process. In
this process, copper-clad laminates are used, the copper claddings except
their predetermined circuit forming portions are masked with a
photosensitive plating-resist, the non-masked portions of copper claddings
are selectively chemical-plated with copper, the plating-resist is then
removed, and the unmasked portions, i.e. the copper claddings except their
predetermined circuit forming portions are removed, thereby making up
circuits.
However, this process still involves the problem that the plating-resist is
liable to peel off during the copper plating hence the formation of good
circuits being impossible. This resist peeling is remarkable in the
chemical copper plating, which gives little variation in the thickness of
plating. In the copper electroplating, the resist peeling is limited,
raising no significant problem in many case. That is whereas the copper
electroplating proceeds quickly and is finished in a short time (in one
hour), the chemical copper plating, proceeding slowly, requires a long
time. for instance, the chemical copper plating to a thickness of 30 .mu.m
requires from 20 to 30 hours, which are at least 10-fold as long as the
time required for the copper electroplating. The plating of such long
duration damages the plating-resist. For example, it is said (IBM J. RES.
DEVELOP, Vol. 29, No. 1 (1985), Cathodic delamination of methyl
methacrylate-based dry film polymers on copper) that a portion of the
chemical copper plating solution permeates along the interface between the
plating-resist and the conductive substrate or through the resist film,
and causes the following reaction:
2H.sub.2 O+O.sub.2 +4e.fwdarw.4OH.sup.-. . . (1)
at the interface, forming hydroxy ions; which result in the rupture of
interfacial bond. In particular, the chemical copper plating bath, having
an alkalinity as high as about 12 in pH, tends to cause the interfacial
destruction.
In order to solve the above noted problem, a measure is proposed which, as
described in the above IBM journal, comprises polishing the surface of
copper cladding with pumice or the like to smooth the surface, and
treating the polished surface with benzotriazole or some other reagent,
followed by applying a photosensitive plating-resist to mask the copper
cladding except its predetermined circuit forming portion. About the case
where copper electroplating is employed instead of chemical copper
plating, Japanese Patent Publication No. Sho. 50-9177 proposes the measure
of adding benzotriazole or the like to a photosensitive plating-resist.
These measures have greatly overcome the problem of the plating-resist
delamination from substrates.
Sometimes, the use of benzotriazole as stated above achieves insufficient
effect or in the chemical copper plating, produces adverse effects on
plating performance. More specifically, the presence of benzotriazole may
lower the rate of plating locally or throughout the whole plating surface
and/or may result in plating films of inferior properties. This is assumed
to be caused by the elusion of benzotriazole into the chemical copper
plating solution. When such adverse effects are produced, no sufficiently
reliable circuit will be obtainable or in certain cases the circuit
formation itself will be impossible. It is considered that the proper
control of benzotriazole concentrations in the resist and on the substrate
surface is indispensable in order to preclude such difficulties as stated
above, but in practice this control is difficult.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process for producing
printed circuit boards which is an improvement of the chemical copper
plating pattern process employing copper-clad insulating boards, wherein
the plating-resist adheres securely to the substrative metal layers,
whereby fine circuits can be formed without causing the delamination of
plating-resist during the chemical copper plating.
The above and other objects of the present invention can be achieved with
each of the following processes:
(1) A process for producing printed circuit boards which comprises the
steps of
(a) roughening a surface of a copper layer formed on an insulating board,
(b) coating the roughened surface of copper layer with a photo-resist layer
containing a sublimable copper-corrosion inhibitor, exposing the resist
layer selectively to actinic rays according to the circuit pattern to
form, and developing the resulting resist, thereby forming plating-resist
coats on circuit-negative pattern portions of the copper layer, that is,
on portions of the copper layer which form no circuit,
(c) heat-treating the plating-resist coats,
(d) plating chemically the circuit-corresponding portion with copper,
(e) removing the plating-resist coats, and
(f) removing the copper layer except the circuit-corresponding portion
thereof.
(2) A process for producing printed circuit boards which comprises the
steps of
(a) roughening a surface of a copper layer formed on an insulating board,
and covering the roughened surface with a thin film of metal having a more
negative reduction potential of oxide than that of copper,
(b) coating the thin metal film surface with a photo-resist layer
containing a sublimable copper-corrosion inhibitor, exposing the resist
layer selectively to actinic rays according to a circuit pattern to form,
and developing the resulting resist, thereby forming plating-resist coats
on circuit-negative pattern portions of the thin metal film,
(c) heat-treating the plating-resist coats,
(d) plating chemically the circuit-corresponding portion with copper,
(e) removing the plating-resist coats, and
(f) removing the thin metal film and the copper layer except their
circuit-corresponding portions.
(3) A process for producing printed circuit boards which comprises the
steps of
(a) roughening a surface of a copper layer formed on an insulating board,
and oxidizing and then reducing the roughened surface of copper layer,
(b) coating the thus treated surface of copper layer with a photo-resist
layer containing a sublimable copper-corrosion inhibitor, exposing the
resist layer selectively to actinic rays according to a circuit pattern to
form, and developing the resulting resist, thereby forming plating-resist
coats on circuit-negative pattern portions of the copper layer,
(c) heat-treating the plating-resist coats,
(d) plating chemically the circuit-corresponding portion
(e) removing the plating-resist coats, and
(f) removing the copper layer except the circuit-corresponding portion
thereof.
(4) A process for producing printed circuit boards which comprises the
steps of
(a) roughening a surface of a copper layer formed on an insulating board,
oxidizing and then reducing the roughened surface of copper layer, and
covering the thus treated surface with a thin film of metal having a lower
normal electrode potential than that of copper,
(b) coating the thin metal film surface with a photo-resist layer
containing a sublimable copper-corrosion inhibitor, exposing the resist
layer selectively to actinic rays according to a circuit pattern to form,
and developing the resulting resist, thereby forming plating-resist coats
on circuit-negative pattern portions of the thin metal film,
(c) heat-treating the plating-resist coats,
(d) plating chemically the circuit-corresponding portion with copper,
(e) removing the plating-resist coats, and
(f) removing the thin metal film and the copper layer except their
circuit-corresponding portions.
(5) A process for producing printed circuit boards as set forth in any of
the above items (1)-(4), wherein the sublimable copper-corrosion inhibitor
is selected from benzotriazole, methylbenzotriazole, benzoguanamine,
guanidine, 1-cyanoguanidine, thiazole, thiourea, 2-quinolylamine,
1,1'-azonaphthalene, dicyclohexylamine nitrite, diisopropylammonium
benzoate, cyclohexylamine benzoate, and dicyclohexylammonium
cyclohexane-carboxylate.
(6) A process for producing printed circuit boards as set forth in any of
the above items (1)-(5), wherein the heating of plating-resist coats is
conducted at a temperature where no deformation of the resist coats takes
place.
(7) A process for producing printed circuit boards as set forth in any of
the above items (1)-(5), wherein the heating of plating-resist coats is
conducted at a temperature of 100.degree. to 180.degree. C. for a period
of 1 to 2 hours.
(8) A process for producing printed circuit boards as set forth in any of
the above items (1)-(4), wherein the removal of the copper layer and the
thin metal film except their circuit-corresponding portions, in the step
(f), is carried out after the copper circuit pattern has been covered with
a etching-resist layer.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a diagram showing the steps of process for producing printed
circuit boards which is an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
A feature of the present invention is to roughen surfaces of copper layers
formed on insulating boards. Another feature of the invention is to
incorporate a sublimable copper-corrosion inhibitor into photosensitive
plating-resist coats on the circuit-negative pattern portions of the
roughened surfaces. A further feature of the invention is to heat the
plating-resist coats before copper circuits are formed by chemical copper
plating.
Conventionally, it has been regarded as a point to make such copper layer
surfaces smooth as far as possible. Polish with pumice is known as a
method for the smoothing. However, such smoothing methods are
unsatisfactory to achieve the sufficient adhesion of plating-resist coats
laminated on copper layers. Good results have been obtained by roughening
rather than smoothing copper layer surfaces. It is considered that the
roughening increases the contact surface area between the copper layer and
the plating-resist and additionally produces anchor effect, thereby the
adhesion being improved.
Further it has been found that when a thin layer of nickel, zinc, tin, or
certain other metal is formed on the roughened surface of copper layer,
the adherence of plating-resist to the substrate is much improved and the
resist coats are kept stable without delamination during the chemical
copper plating. From results of investigating the delamination of
plating-resist during the plating, it can be considered that said good
adherence of plating-resist is caused by a superficial oxide film which,
covering said thin metal layer, is not reduced by the plating solution
that has penetrated to the interface. That is, it is assumed that oxides
of metals such as nickel, zinc, and tin, because the reduction potentials
of these metal oxides are more negative than the reaction potential of the
chemical copper plating solution, are retained without undergoing
reduction and hence the bond between the plating-resist and the thin metal
layer will not be split.
As stated above, the present invention is featured in that the process
thereof includes the step of forming a photo-resist layer containing a
sublimable copper-corrosion inhibitor, exposing the photo-resist layer to
actinic rays, and developing the photo-resist layer to form plating-resist
coats on the substrate portions (negative pattern portions) other than the
predetermined circuit forming portion of the substrate and the step of
heat-treating the plating-resist coats. It has been confirmed that when a
photo-resist containing benzotriazole is used as a resist to chemical
copper plating, the delamination of resist is reduced to a great extent as
in the copper electroplating. But, the addition of benzotrizole, as stated
before, raises the problems of inferior properties of copper films formed
by chemical plating and lower rates of plating and the optimum amount of
benzotriazole to add is difficult to determine. Hence, it has been
substantially impossible to realize the addition of benzotriazole. In
particular, when the chemical plating is repeated by using a copper
plating solution without exchanging it or when the surface area of
plating-resist coat is large, benzotriazole is eluted into the plating
solution and accumulated therein, and eventually the plating becomes
substantially impossible.
As a result of extensive investigations, the present inventors have found
that copper-corrosion inhibiting substances other than benzotriazole, when
incorporated into photosensitive plating-resists, are effective, similarly
to benzotriazole, in preventing the delamination of resist coats. However,
it has also been found that these other copper-corrosion inhibitors,
similarly to benzotriazole, eluted into the chemical, copper plating
solution, lowers the rate of plating and/or results in deteriorated
plating film properties. Further investigations made thereupon have
revealed that th contamination of the chemical copper plating solution and
the delamination of plating-resist coats can be prevented simultaneously
by forming resist coats containing a sublimable copper-corrosion inhibitor
and then heating the resist coats. Based on this finding, the present
invention has been accomplished.
It is conceivable that the heat treatment may sublime a part of the
sublimable copper-corrosion inhibitor, leaving a proper amount thereof in
the resist coat, thereby achieving said favorable effects. Presumably, the
concentration of copper-corrosion inhibitor remaining in the resist coats
has such a gradient as to be higher on the copper layer side and lower on
the plating solution side.
According to the above described manner of carrying out the present
invention, fine circuit patterns can be formed without suffering the
problem of resist coat delamination under much severer conditions of
chemical copper plating than those of copper electroplating and with less
contamination of the chemical copper plating solution, the life of which
is markedly prolonged.
Referring now to FIG. 1, the present invention is described more
specifically.
FIG. 1 (a) shows the surface-roughened state of a copper layer 2 sticked on
an insulating board 1. Materials adaptable for the insulating board 1
include glass epoxy laminates, glass polyimide laminates, and ceramic
boards. Usual copper-clad laminate can be used as the copper layer 2 and
the insulating board 1. Thinner copper layers are favorable for fine
circuit fabrication. The surface of copper layer 2 can be roughened by
mechanical methods such as sandblasting or chemical methods using
solutions such as aqueous cupric chloride solutions acidified with
hydrochloric acid. An effective method for further roughening the s rface
is to treat it with an aqueous sodium chlorite solution or the like and
subsequently with an aqueous dimethylamino borane solution or the like. In
this invention, the copper surface is once oxidized to form copper (II)
oxide, which is then reduced to metallic copper, whereby the surface is
roughened, forming fine projections and depressions (Japanese Patent
Application Kokai No. Sho 61-176192).
For the purpose of securing the adhesion of plating-resist during the
plating, it is preferable to conduct such oxidation and reduction
treatments of the copper surface. When better adhesion is required for
plating-resist coats, a thin metal film 3 is formed on the roughened
copper surface as shown in FIG. 1b. Preferred metals are of the type
having a more negative oxide film reduction potential than the reaction
potential of the chemical copper plating solution Particularly metals
fitted for this film 3 are nickel, zinc, chromium, tin, and alloys of
these metals. Particularly. While FIG. 1 shows the fabrication of
single-sided printed circuit boards, the present process is adaptable for
the fabrication of double sided or multilayer printed circuit boards. In
this case, plating of through holes can be carried out as occasion
demands.
After roughening of the copper layer surface, the copper layer except the
predetermined circuit forming portion thereof is masked with a
plating-resist 4 as shown in FIG. 1c. This plating-resist may be a
negative type photo-resist containing a sublimable copper-corrosion
inhibitor. Suitable photo-resists for use in the present invention include
photo-polymerizable unsaturated compounds having a ethylenic unsaturated
bond at terminals (vinyl or isopropenyl groups). Examples of such
unsaturated compounds are acrylic esters and methacrylic esters of
polyhydric alcohols such as trimethylolpropane, trimethyhlolethane,
propylene glycol, and tetraethylene glycol.
Examples of the sublimable copper-corrosion inhibitor include
benzotriazole, methylbenzotriazole, benzoguanamine, guanidine,
1-cyanoguanidine, thiazole, thiourea, 2-quinolylamine,
1,1'-azonaphthalene, dicyclohexylamine nitrite, cyclohexylaminobenzoate,
diisopropylammonium benzoate, and dicyclohexylammonium
cyclohexane-carboxylate. Suitable contents of the sublimable
copper-corrosion inhibitor in the photoresist depend upon the kind of
inhibitor itself and conditions of the after-heating. In the case of
benzotriazole, the suitable contents thereof are from 0.01 to 1 part by
weight per 100 parts by weight of the photoresist and the after-heating is
desirably carried out at a temperature of 100.degree. to 160.degree. C.
for a period of 1 to 2 hours. It is desirable to add the copper-corrosion
inhibitor in such an amount that the performance characteristics of the
photo-resist may not be impaired as far as possible by the inhibitor.
The photosensitive plating-resist is laminated in film form on the
roughened surface stated above by the common method. The lamination of
resist film is followed by removing its portion laid on the predetermined
circuit portion of the substrate. In general, this photoengraving is
carried out in the manner that said circuit-corresponding portion of the
photo-resist is masked, the non-masked portions are exposed to actinic
rays, and the photo-resist coat is developed by using a liquid developer
such as Chlorothene. In this case, excessive exposure may raise problems
such that the exposed resist is difficult to remove in a later step and
that the object of the present invention cannot be achieved sufficiently.
Proper quantities of light for the exposure depend upon the kinds of light
source and resist. When an ultra high pressure mercury lamp is used as a
light source, the proper light quantities are up to 300 mJ/cm.sup.2.
In the next place, the after-heating is car ied out. Suitable conditions of
this after-heating depend upon the kind and amount of copper-corrosion
inhibitor contained in the photosensitive plating-resist. The
after-heating is conducted desirably at a temperature where the patterned
resist does not deform or undergo denaturation. In many cases the
after-heating temperature is up to 180.degree. C. This after-heating
sublimes an excess of the copper-corrosion inhibitor to remove it, whereby
such a distribution of the inhibitor concentration as sated above (the
concentration is higher on the copper layer side and lower on the outer
side) is presumably formed (the concentration measurement is not made).
When the thin metal layer 3 has been formed, the circuit-corresponding
portion thereof is then removed, as shown in FIG. 1d, as occasion demands.
Most of the liquids which dissolve the metal layer 3 can be used for this
removal.
Thereafter the circuit-corresponding portion of copper layer is plated
chemically with copper 5 as shown in FIG. 1e. For this chemical copper
plating, usual thick-plating solutions are adaptable. When through holes
are chemically plated with copper, it is desirable to form a plating film
of specially high quality. High quality plating films superior in
elongation and other properties can be obtained by plating at 70.degree.
C. for several to tens of hours using, for example, a chemical copper
plating solution of the following composition:
______________________________________
CuSO.sub.4 0.04 M
Ethylenediaminetetracetic acid
0.08 M
(EDTA)
HCHO 0.03 M
NaOH quantity to give pH 12.6
2,2'-dipyridyl 30 mg/l
Polyethylene glycol
10 g/l
______________________________________
After completion of the chemical copper plating, a solder plating 6, which
serves as an etching resist for copper, is formed on the copper plating as
shown in FIG. 1f. However, this plating is not necessary formed of solder
but may be formed of gold, nickel, or some other metal. If this etching
resist for copper is not formed, the copper layer portion to form the
intended circuit will be partly removed by the copper etching (to remove
the unnecessary portions of the copper layer) in a later step. Hence the
etching resist 6 for copper is preferably formed, When the etching resist
for copper is formed of a solder plating, generally-used fluoroborate
plating solutions are available.
After completion of the solder plating, the photo-resist coats 4 are
removed as shown in FIG. 1g. Since this step of removing the photo-resist
coats is indispensable in the present invention, it is desirable to omit
the after-exposure that is effective for accelerating the hardening of the
resist after development. common peeling liquids such as methylene
chloride may be used for the removable of resist coats.
After the photo-resist coats have been removed, the copper layer 2 except
its portion serving as the intended circuit is removed by etching as shown
in FIG. 1h. When the metal layer 3 is formed previously, the unnecessary
portions thereof are removed similarly. Finally, the solder plating 6k,
which is an etching resist for copper, is removed as shown in FIG. 1i.
However, when this removal is unnecessary, the operation may be ended with
the state of FIG. 1h left as such. In particular, when the etching resist
for copper is formed of a gold plating, it is after left as such without
removal.
It is possible by carrying out the above desoribed process to fabricate a
printed circuit board having a fine circuit pattern without causing any
defect in the adherence of plating-resist coats to the substrate during
the chemical copper plating and without substantial contamination of the
chemical copper plating solution.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is illustrated in more detail with reference to the
following examples.
EXAMPLE 1
Step a: Through holes were drilled at necessary positions of a glass epoxy
laminate having on either side thereof a 18-.mu.m thick copper cladding.
Then the copper surfaces were polished by brushing, degreased with alkali,
washed with water, and treated with a soft etching solution at 30.degree.
C. for 1 minute. The etching solution was previously prepared by
dissolving 200 g of ammonium persulfate and 10 ml of sulfuric acid in
water to give a whole volume of 1 l. After washing, the laminate was
dipped in 15% hydrochloric acid for 1 minute and then in a catalyst liquid
(tradename: HS101B, supplied by Hitachi Kasei Kogyo Co., Ltd.) at
20.degree. C. for 5 minutes, washed with water, further dipped in 15%
hydrochloric acid at 230.degree. C. for 5 minutes, and washed with water,
thus activating both the surfaces. Subsequently, the laminate was plated
with copper in a chemical plating solution of the following composition
(I) at 70.degree. C. for 2 hours.
______________________________________
Composition (I)
______________________________________
CuSO.sub.4.5H.sub.2 O
10 g/l
Disodium ethylenediaminetetra-
30 g/l
acetate dihydrate
Formalin (37%) 3 ml/l
NaOH Amount to give pH 12.6
2,2'-Dipyridyl 30 mg/l
Polyethylene glycol
10 g/l
(average molecular weight 600)
______________________________________
The through holes drilled in the plated laminate at necessary positions
were also plated by the above chemical copper plating to connect
electrically the both side copper layers to each other.
Step b: To roughen the surface of each copper layer, the copper-clad
laminate was dipped in a solution of the following composition (II) with
stirring by aeration at 45.degree. C. for 30 seconds.
______________________________________
Composition (II)
______________________________________
CuCl.sub.2.2H.sub.2 O
40 g/l
HCl (36%) 500 ml/l
______________________________________
Then the plating surface was washed with water, thus preparing a
surface-roughened base board.
Step c: The surface of base board was thoroughly dried. On the other hand,
a photosensitive resin solution of the following composition (III) was
applied uniformly on a 25-.mu.m thick polyethylene terephthalate film, and
the coating was dried in a hot air convection type oven of 80.degree. C.
for 10 minutes.
______________________________________
part
Composition (III) by weight
______________________________________
Trimethylolpropane triacrylate
20
Tetraethylene glycol diacrylate
20
Polymethyl methacrylate 60
(weight average molecular weight about 120,000)
Benzophenone 6
4,4'-Bis(diethylamino)benzophenone
0.1
Benzotriazole 0.1
Victoria Pure Blue 0.05
Hydroquinone 0.1
Methyl ethyl ketone 100
Toluene 50
______________________________________
The above coating was controlled to give a 35-.mu.m thick layer of
photosensitive resin composition after drying. An about 25-.mu.m thick
polyethylene film was sticked as a cover film on the photosensitive resin
composition layer to prepare a photosensitive film supported by PET film
and covered with PE Film to become subsequently a plating-resist. After
the cover film was separated from the element, the remainder was laminated
on both sides of the above prepared base board by using a hot roll
laminator. This lamination was conducted continuously at a hot roll
temperature of 110.degree. C. and a lamination speed (speed of stock
traveling) of 1 m/min. After the resulting laminate was allowed to cool
for about 5 minutes, its predetermined circuit forming portion was masked,
and the other portions were exposed to 100 mJ/cm.sup.2 of light from an
ultra high pressure mercury lamp. Then the development was made by
spraying 1,1,1-trichloroethane as a developer at about 18.degree. C. for 2
minutes. Thus, the copper layers (on both sides of glass epoxy laminate)
except their predetermined circuit forming portion were masked with
plating-resist coats. In this example a 90 .mu.m thick circuit pattern was
formed on either side of the base board.
Step d: After the copper layers except their predetermined circuit forming
portion have been masked with plating--resist coats, thermal treatment was
conducted at 140.degree. C. for 1 hour.
Step e: The whole of the substrate was immersed in an aqueous solution of
sulfuric acid of 100 ml/l for 2 minutes to remove oxides, etc., and then
washed with water.
Step f: The cleaned board was immersed in a chemical copper plating
solution of the same composition as composition (I) in step (a) at
70.degree. C. for 12 hours, thereby being plated with a pattern of copper.
After plating, the board was thoroughly washed with water.
Step g: The resulting board was dipped in an aqueous solution of sulfuric
acid (100 ml acid/l solution) for 2 minutes, and further immersed in a
solder plating bath containing 15 g/l of sn.sup.2+, 10 g/l of Pb.sup.2+,
40 g/l of H.sub.3 BO.sub.3, and 300 g/l of HBF.sub.4 with stirring for 25
minutes while supplying an electric current at 1A/dm.sup.2, thereby
plating the copper plating pattern with solder. The board was then washed
thoroughly with water and dried.
Thus a double sided printed circuit board having plated through holes was
made up by operating steps a through h in succession.
EXAMPLE 2
A double sided, through holed, printed circuit board was fabricated
according to the procedure of Example 1 except that the following step i
was added between steps b and c.
Step i: To roughen further the surface of each copper layer, the base board
was dipped in a treating solution of the following composition (IV) at
70.degree. C. for two minutes, thereby oxidizing the copper layer surface.
______________________________________
Composition (IV)
______________________________________
NaClO.sub.2 100 g/l
Na.sub.3 PO.sub.4 30 g/l
NaOH 12 g/l
______________________________________
After washing with water, the base board was dipped in a treating solution
of the following composition (V) at 45.degree. C. for 1 minute to reduce
the oxide. Thereby the copper layer surface was roughed sufficiently. The
base board was then washed thoroughly.
______________________________________
Composition (V)
______________________________________
Dimethylaminoborane 10 g/l
NaOH 10 g/l
______________________________________
EXAMPLE 3
A double sided, through holed, printed circuit board was fabricated
according to the procedure of Example 1 except that the following step j
was operated instead of step b.
Step j: To roughen the surface of each copper layer, the copper-clad
laminate was subjected successively to; dipping in an aqueous solution
containing 200 g/l of ammonium persulfate and 5 ml/l of sulfuric acid with
stirring at 30.degree. C. for 1 minute; washing with water; dipping in a
treating solution of composition (IV), as shown in step i of Example 1, at
70.degree. C. for 2 minutes; ashing with water; dipping in a treating
solution of composition (V), as shown in Step i of Example 1, at
45.degree. C. for 1 minute to reduce the oxide; washing with water;
plating in a nickel plating solution of the following composition (VI) at
20.degree. C. and 0.1 A/dm.sup.2 for 6 minutes, thereby forming a thin
nickel layer on the surface of each copper layer; and to sufficient
washing with water.
______________________________________
Composition (VI)
______________________________________
NiSO.sub.4.6H.sub.2 O
200 g/l
NaCl 15 g/l
H.sub.3 BO.sub.3
15 g/l
______________________________________
EXAMPLE 4
A double sided, through holed, printed circuit board was fabricated
according to the procedure of Example 3 except that the content of
benzotriazole in the photosensitive resin solution of composition (III)
used in step c was changed to 0.02 part by weight and that the heat
treatment in step d was conducted at 100.degree. C. for 2 hours.
EXAMPLE 5
A double sided, through holed, printed circuit board was fabricated
according to the procedure of Example 3 except that the content of
benzotriazole in the photosensitive resin solution of composition (III)
used in step c was changed to 0.5 part by weight and that the heat
treatment in step d was conducted at 160.degree. C. for 2 hours.
EXAMPLE 6
A double sided, through holed, printed circuit board was fabricated
according to the procedure of Example 3 except that in step j, zinc
electroplating was conducted by using a zinc plating solution (Schering
bath, supplied by Jincalux Co.) instead of the nickel plating solution at
0.5 A/dm.sup.2 for 5 minutes.
EXAMPLE 7
A double sided, through holed, printed circuit board was fabricated
according to the procedure of Example 3 except that the composition (III)
of the photosensitive resin solution used in step c was changed to the
following composition (VIII) and that the heat treatment in step d was
conducted at 150.degree. C. for 1 hour.
______________________________________
Composition (VIII) Part by weight
______________________________________
Trietoxidized trimethylolpropane
40
triacrylate (tradename: Acryl Monomer
SR-454, supplied by Sartomer Co.)
Methyl methacrylate/ethyl
60
acrylate/dimethylaminoethyl methacrylate
(97/2/1 weight ratio) copolymer (weight
average molecular weight about 100,000)
Benzophenone 6
4,4'-Bis(diethylamino)benzophenone
0.1
Benzoguanamine 0.2
Leuco Crystal Violet 0.3
Tribromomethylphenyl sulfone
0.3
Victoria Pure Blue 0.03
Hydroquinone 0.1
Methyl ethyl ketone 100
Toluene 50
______________________________________
EXAMPLE 8
A double sided, through holed, printed circuit board was fabricated
according to the procedure of Example 7 except that 0.02 part by weight of
1-cyanoguanidine was used instead of benzoguanamine in the photosensitive
resin solution of composition (VIII).
EXAMPLE 9
A double sided, through holed, printed circuit board was fabricated
according to the procedure of Example 7 except that 1 part by weight of
2-quanolylamine was used instead of benzoguanamine in the photosensitive
resin solution of composition (VIII) and that the heat treatment in step d
was conducted at 130.degree. C. for 1 hour.
EXAMPLE 10
A double sided, through holed, printed circuit board was fabricated
according to the procedure of Example 7 except that 5 parts by weight of
cyclohexylamine benzoate was used instead of benzoguanamine in the
photosensitive resin solution of composition (VIII) and that the heat
treatment in step d was conducted at 130.degree. C. for 1 hour.
Results of Examples 1-10 together with those of the following comparative
examples are summarized in Table 1. As are evident from Table 1, good
results were obtained in all of Examples 1-10.
Comparative Example 1
A double sided, through holed, printed circuit board was fabricated
according to the procedure of Example 3 except that benzoytriazole was not
incorporated into the photosensitive resin solution of composition (III)
used in step (c) and that the heat treatment in step d was omitted.
Comparative Example 2
A double sided, through holed, printed circuit board was fabricated
according to the procedure of Example 3 except that the heat treatment in
step d was omitted.
Comparative Example 3
A double sided, through holed, printed circuit board was fabricated
according to the procedure of Example 3 except that benzoytriazole was not
incorporated into the photosensitive resin solution of composition (III)
used in step c.
Comparative Example 4
A double sided, through holed, printed circuit board was fabricated
according to the procedure of Example 3 except that the formation of thin
metal film in step j was omitted.
TABLE 1
__________________________________________________________________________
After heat
Photo-resist coat treatment
Copper-corrosion inhibitor
Tempera-
Metal
Base Content
ture Period
Roughening film
composition
Chemical name
(part by wt)
(.degree.C.)
(hr)
__________________________________________________________________________
Example
1 Composition (II)
-- Composition
Benzotriazole
0.1 140 1
No. (III)
2 Compositions (II),
-- Composition
Benzotriazole
0.1 140 1
(IV), (V) (III)
3 Ammonium persulfate
Ni Composition
Benzotriazole
0.1 140 1
compositions (IV) (V)
(III)
4 Ammonium persulfate
Ni Composition
Benzotriazole
0.02 100 2
compositions (IV) (V)
(III)
5 Ammonium persulfate
Ni Composition
Benzotriazole
0.5 160 2
compositions (IV) (V)
(III)
6 Ammonium persulfate
Zn Composition
Benzotriazole
0.1 140 1
compositions (IV) (V)
(III)
7 Ammonium persulfate
Ni Composition
Benzoguanamine
0.2 150 1
compositions (IV) (V)
(VIII)
8 Ammonium persulfate
Ni Composition
1-Cyanaguanidine
0.02 150 1
compositions (IV) (V)
(VIII)
9 Ammonium persulfate
Ni Composition
2-Qunolyamine
1 130 1
compositions (IV) (V)
(VIII)
10 Ammonium persulfate
Ni Composition
Cyclohexylamine
5 130 1
compositions (IV) (V)
(VIII) benzoate
Compara-
1 Ammonium persulfate
Ni Composition
-- -- -- --
tive compositions (VI) (V)
(III)
Example
2 Ammonium persulfate
Ni Composition
Benzotriazole
0.1 -- --
No. compositions (IV) (V)
(III)
3 Ammonium persulfate
Ni Composition
-- -- 140 1
compositions (IV) (V)
(III)
4 -- -- Composition
Benzotriazole
0.1 140 1
(III)
__________________________________________________________________________
Adherence of resist coat during
Rate of*.sup.2
Elongation*.sup.3
plating plating
of plating film
(degree of delamination)*.sup.1
(.mu.m/h)
(%)
__________________________________________________________________________
Example
1 Generally good (2%)
2.9 5.7
No. 2 Generally good (2%)
3.1 4.8
3 Good (up to 1%)
3.1 6.3
4 Good (up to 1%)
3.0 7.4
5 Good (up to 1%)
2.8 4.9
6 Good (up to 1%)
2.9 5.3
7 Good (up to 1%)
2.8 6.0
8 Good (up to 1%)
3.0 7.1
9 Generally good (2%)
3.1 7.7
10 Generally good (2%)
3.2 7.9
Compara-
1 Slightly bad (20%)
3.1 5.1
tive 2 Good (up to 1%)
1 or below
1 or below
Example
3 Bad (30%) 3.0 6.3
No. 4 Bad (30%) 3.1 6.8
__________________________________________________________________________
Notes
*.sup.1 Degree of delamination = Ratio (%) of delamination area to whole
interfacial area of resist coat.
*.sup.2 Rate of plating = Average value = Final thickness of
plating/plating type period (the plating thickness was measured with a
coulometric thickness tester).
*.sup.3 Elongation of plating film applied on stainless steel sheet (the
plating film was gradually peeled from the stainless steel sheet by using
a tensile tester and the elongation at break was measured with the
tester).
Effect of the Invention
According to the present invention; photosensitive plating-resist coats
good in adherence to substrates and hence free from delamination during
chemical copper plating can be obtained and substantially no
copper-corrosion inhibitor is eluted from the plating-resist coats into
chemical copper plating solutions; hence good chemical copper plating
patterns can be formed without causing drop in the rate of plating or
deterioration of plating film properties. Thus the process of the present
invention is much effective in the fabrication of fine circuit patterns.
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